Many apparatuses have been developed to apply a coating of solder to the underside of an advancing substrate, such as a printed circuit board for the purpose of solder bonding elements mounted on or projecting through the board to metallic circuit paths or pads on the board. In certain manufacturing processes it is necessary that the solder stream or wave be applied as a thin stripe along the undersurface of the advancing substrate. In one such process, a connector housing is mounted on one edge of a circuit board with projecting connector terminals overlaying and mechanically engaging metallic circuit pads adhered to the circuit board. The board is then placed in a conveyor fixture and advanced through a solder wave having a width sufficient to lay a stripe of molten solder on the overlaying terminals and contact pads to effectuate the solder bonding of the terminals to the contact pads.
In copending patent application Ser. No. 481,088, filed Mar. 3, 1983, in the names of W. C. Kent and C. H. Payne now U.S. Pat. No. 4,527,731, there is disclosed methods and apparatus for applying solder stripes to mechanically assembled connectors and printed circuit boards. More specifically in this copending application a connector is assembled on one edge of a small printed circuit board with the connector terminals overlaying circuit board contact pads whereafter the assembled board and connector are advanced along the inclined top surfaces of a pair of channel members constructed of non-solder wetting material. A solder stream is created by pumping a series of contiguous solder jets which are flowed between the channel members so that the top of the stream forms a meniscus projecting above the level of the tops of the inclined channel members to apply a thin solder stripe to the overlaying terminals and metallic contact pads.
The instant application utilizes similar apparatus but is concerned with more precisely maintaining the temperature of and the height of the solder stream. With variations in temperature, non-uniform solder bonds are often encountered and with variations in the height of the solder stream, there are possibilities of the solder stream overflowing the channel members and flowing onto sections of the circuit board that must be maintained free of solder. Accordingly, the present invention provides a method of more precisely controlling the temperature of the molten solder as well as controlling the height of the solder stream to insure application of sufficient solder while preventing solder overflow and subsequent damage to the circuit board and any electrical components mounted therein.